Dry skin is one of the most significant cosmetic problems in today's population. It is caused by a reduction in both the water content and the lipid content of the skin. The two main approaches which have been taken in the past to moisturize skin are: (1) to apply compositions containing hygroscopic materials to the skin in order to attract and hold water on the skin's surface, and (2) to apply compositions containing oily materials which form a barrier on the skin and thereby reduce transepidermal water loss through the skin. In the latter case, the water level is thought to build up in the skin layer beneath the barrier. Today, the most accepted approach to moisturization involves the use of both methods simultaneously. Most of the moisturizing products in the marketplace today consist of oil-in-water emulsions and creams, water-in-oil emulsions and, to a lesser degree, simply 100% oil formulations. These compositions generally use oils as the main moisturizing ingredient with lesser amounts of humectants. The oils are selected from a large group of commercially available, cosmetically accepted oils, which are generally recognized by the cosmetic industry as having emollient properties.
While these moisturizing products do work, their effects are not long-lasting, i.e., they have to be used repeatedly in order to provide a maximum moisturizing benefit. This is primarily due to the fact that the moisturizing oils do not remain on the skin's surface long enough. Surfactants present in the compositions tend to increase their water-removability.
According to the present invention, it has been discovered that certain oil-soluble acrylate polymers, in combination with conventional moisturizing oils, in an oil-in-water emulsion, provide improved cosmetically-acceptable moisturizing compositions which are substantive to skin, i.e., they are not readily removed by simple abrasion or water assault.
Oil-soluble acrylate polymers have been used heretofore in sunscreening compositions of the oil or water-in-oil type to reduce removal of the sunscreening agent from the skin by swimming or perspiration. Such compositions are described in U.S. Pat. No. 4,172,122.
Other cosmetic compositions containing oil-soluble acrylate polymers include make-up compositions such as lip rouges and mascara disclosed in U.S. Pat. No. 3,911,105, eyeliners and mascaras disclosed in Japanese Patent Application (Publication No.) 54-151139; and eyeliners disclosed in Japanese Patent Application (Publication No.) 55-130907.
Water-in-oil emulsion compositions for skin treatment containing low molecular weight oil-soluble acrylate copolymers as emulsifying agents are disclosed in U.S. Pat. Nos. 4,057,622; 4,057,623; 4,057,624; 4,128,634; 4,128,635; 4,128,636. However, prior to the present invention, it had not been recognized that the addition of certain oil-soluble acrylate polymers to oil-in-water emulsions containing emollient oils and surfactants results in compositions having improved, long-lasting skin moisturizing effects.